1. Field of the Invention
The present invention relates to a sheet post-processing apparatus which receives sheets discharged from an image forming apparatus such as an electrophotographic copying machine, printer, facsimile apparatus, or a composite machine having these functions, and executes postprocessing such as a folding process.
2. Description of the Prior Art
Recently, various kinds of sheet postprocessing apparatuses have been proposed, which bundle and align a plurality of sheets on which image are recorded by an image forming apparatus such as a copying machine, and perform postprocessing such as binding and folding with respect to the aligned sheet bundle.
For example, as a sheet postprocessing apparatus for manufacturing a booklet by saddle-stitching the middle portion of this sheet bundle and center-folding the sheet bundle at the saddle-stitched portion, the apparatuses disclosed in Japanese Unexamined Patent Publication Nos. 10-181990 and 2001-2317 are known.
These sheet postprocessing apparatuses have a folding unit constituted by a pair of center folding rollers which rotate in tight contact with each other to fold a sheet bundle and a center folding plate which pushes the saddle-stitched portion of the sheet bundle to the press portion between the center folding rollers.
A sheet postprocessing apparatus having a folding unit for folding a sheet into three is disclosed in Japanese Unexamined Patent Publication No. 2002-60127. This sheet postprocessing apparatus forms a sealed document such as postal matter or direct mail by sealing or inserting one or a small number of three-folded sheets into an envelope.
A Z-fold apparatus is known, which forms the first crease on a sheet along a direction (width direction) perpendicular to its longitudinal direction, center-folds the sheet, and forms the second crease which is formed parallel to the first crease on the center-folded sheet and is used to fold back the sheet to the opposite side to the first folding side, thereby folding the sheet into three. A large-sized sheet is Z-folded and reduced in size to ½ or less by this Z-fold apparatus. The Z-folded sheet can therefore be stored in a small-sized file or the like. Unfolding this sheet allows an easy visual check.
When, however, the above Z-fold process is to be performed, a Z-fold apparatus must be connected to an image forming apparatus independently of a conventional sheet postprocessing apparatus designed to perform postprocessing such as a center folding process or three-fold process or must be singly installed in the image forming apparatus.
As described above, according to the prior art, an image forming system for separately performing postprocessing including a center folding process, three-fold process, and Z-fold process with respect to sheets discharged from an image forming apparatus is formed by connecting a Z-fold apparatus to the image forming apparatus in addition to the conventional sheet postprocessing apparatus for performing postprocessing including a center folding process and three-fold process.
In such an image forming system, the structure of the sheet postprocessing apparatus including the Z-fold apparatus becomes complicated, resulting in a high manufacturing cost.